OLETs are a recent type of light emitting devices that is attracting increasing attention compared to other devices such as organic light emitting diodes (OLEDs) due to their ease of manufacturing, high brightness and other improved features. See Muccini at al, “Organic light-emitting transistors with an efficiency that outperforms the equivalent light-emitting diodes,” Nature Materials, 9: 496-503 (2010).
More information on the relevant development of OLET structures may also be found in U.S. Pat. No. 8,497,501, European Patent Publication No. 2737559, European Patent Publication No. 2574219, European Patent Publication No. 2583329, and European Patent Publication No. 2786437.
All the above-identified patent documents are related to OLET structures, i.e., the light emitting devices, but not to specific architectures and solutions for making display pixels.
U.S. Patent Publication No. 2013/0240842 describes a certain pixel architecture for OLET-based displays. More specifically, the described architecture includes a vertical organic field effect transistor (VFET) coupled to a vertical organic light emitting transistor (VOLET), where the VFET functions as a switching transistor and where the VOLET functions as a driving transistor that is also configured to emit light in response to activation by the switching transistor. Because organic semiconductors generally have low output currents compared to silicon semiconductors, one way to achieve high output current using organic semiconductors is to shorten the channel length. In the conventional lateral channel thin film transistor design (in which the source and drain electrodes are laterally displaced from each other), shortening the channel length involves placing the source and drain electrodes very close to each other which can be expensive due to the need for high resolution patterning. In a vertical field effect transistor (in which the source and drain electrodes are provided in a vertically overlapping manner), however, the channel length is defined by the thickness of the semiconductor thin film channel layer, which allows submicron channel lengths without using high resolution patterning. Thus, U.S. Patent Publication No. 2013/0240842 attempts to address the shortcomings of lateral channel thin film transistors by using a VFET as the switching transistor for an OLET instead.